Function combine_ty_args 

pub fn combine_ty_args<Infcx, I, R>(
    infcx: &Infcx,
    relation: &mut R,
    a_ty: I::Ty,
    b_ty: I::Ty,
    variances: I::VariancesOf,
    a_args: I::GenericArgs,
    b_args: I::GenericArgs,
    mk: impl FnOnce(I::GenericArgs) -> I::Ty,
) -> RelateResult<I, I::Ty>
where
    Infcx: InferCtxtLike<Interner = I>,
    I: Interner,
    R: PredicateEmittingRelation<Infcx>,